Please help ""linear variable capacitor transducer" homework

Discussion in 'Homework Help' started by hnc dave, Oct 18, 2012.

  1. hnc dave

    Thread Starter New Member

    Oct 18, 2012
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    BELOW IS A BLOCK DIAGRAM OF A.........
    LINEAR VARIABLE CAPACITOR TRANSDUCER.........,
    ON WHICH I HAVE TO WRITE A REPORT ON EXPLAINING WHAT EACH BLOCK IS AND ITS INPUT AND OUTPUT RELATIONSHIPS TO EACH BLOCK , ANY HELP WOULD BE GREATLY APPRECIATED GUYS , THANKS

    [​IMG]
     
  2. hnc dave

    Thread Starter New Member

    Oct 18, 2012
    10
    0
    The first block is the biggest problem , it has a power supply and a frequency of 40 khz but im not sure if its generating this or recieving it ,, what do u guys think ,,, and can anyone tell me what the block diagram may represent as an electronic device ,, thanks
     
  3. hnc dave

    Thread Starter New Member

    Oct 18, 2012
    10
    0
    heres what i think personnally but im not to sure guys

    FROM RIGHT TO LEFT



    1st Box is a signal generator that outputs an Alternating Current signal at up to 40KHz = 40,000 sine waves a second at a few volts. Hunterston generates 230V @ 50Hz. Radio 2 comes to us at 88.5 MHz = 88,500,000 sine waves a second.

    Box 2 is a variable capacitor - two sets of co-axial plates that mesh with each other (not touching) to form a varying capacity which in this case looks as though it will fine tune what block one is producing.

    Box 3 is just an amplifier that will make the sine wave bigger in voltage.

    Box 4 is a Bandpass Filter that will only allow certain frequencies through.

    Box 5 is a rectifier - in this case a full wave rectifier. Regard it as a set of valves that allow current to pass one-way. In this case the valves (diodes) will let through both the positive going parts of the sine wave, flip over the negative going parts and output a steadyish Direct Current voltage - like what you get from a battery. This box would have a reservoir capacitor to help smoooth out what the diodes let through.

    Box 6 is a differential amplifier which will allow output when certain criteria is met by the two inputs. Used, in this case, I think to allow zeroing or calibration of the system.

    Box 7 another amplifier to make voltage bigger to drive whatever it is needed for.

    Box 8 display? Could be a simple meter to show that voltage output.
    Right arrow - DC volts going to whatever is being controlled







    AM I CLOSE OR WAY OFF THE MARK??
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,646
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    Hello,

    For BOX 2 , the variable capacitor:
    What happens with the AC resistance when the capacitance changes?
    How will this influence the signal from the 40 kHz generator to the amplifier?

    Bertus
     
  5. AHandy1

    New Member

    Jan 14, 2013
    2
    0
    Hello Dave and all,
    I feel I could add my 5 cents here.
    This block diagram appears to be something like a throttle position or fluid level sensor or any other similar application requiring reliability/durability and safety features, as it is not utilizing any contacts to measure linear motion/position. Instead it uses a capacitance that varies with position of a mechanism. As you may know, any capacitor exhibits resistance to an AC signal and therefore will be acting as varying resistor. Given that frequency stays the same and capacitance changes, it will produce varying signal(voltage) at the output of the full wave rectifier. Filters and amplifiers help to condition and scale up/down the signal. After rectifier the signal(voltage) is compared to the reference(adjustable voltage source). The difference is used to produce and display the result such as numerical and/or graphical representation of the Fluid level or throttle position.
    I hope this is what you asked for.
    Best.
     
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    You also need to think about the input impedance of the AC amplifier. What if it is (nearly) infinite?
     
  7. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    It appears to me to be a pulsed sonar block diagram for finding the depth of water. The transducer is submerged, pulsed on, pulsed off, and waits for echo which is then amplified.

    Perhaps what the P inputs are, the pulse, for synchronization, and the S is the return signal. The remaining amplification allows for a display output based upon depth or return type (soft/hard/etc).

    Just a guess.
     
  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    What would the purpose of the linear variable capacitor?
     
  9. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    I'm guessing tuning for the piezo element to match impedance with whatever the transducer is submerged in or similar. It could be the transducer itself with a trimmer.
     
  10. BillB3857

    Senior Member

    Feb 28, 2009
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    I think the tags are P=Power, S=Signal. Are we really trying to do the homework for the OP. Lets have him describe his thoughts on each block and then clarify if needed. After all, this is the HOMEWORK HELP section. Not the HOMEWORK DO IT FOR ME section.
     
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